Oxidative stress represents an imbalance between cellular reactive oxygen species (ROS) production and cellular responses to ROS such as degrading ROS species and producing endogenous anti-oxidant molecules.
ROS serve critical cellular signaling needs, but can have deleterious effects if overproduced or left unchecked. Increased ROS levels in a cell can result in damage to components such as lipids, proteins, polysaccharides, and DNA. Prolonged oxidative stress is also linked to chronic diseases that affect nearly every major organ system. For example, prolonged oxidative stress is implicated in the onset or progression of disease states such as neurodegenerative diseases, lung diseases, cardiovascular diseases, renal diseases, diabetes, inflammatory pain, and cancer. Accordingly, strategies to mitigate oxidative stress are desirable for a number of therapeutic settings.
Under normal physiological conditions, production of ROS is counterbalanced by a well-defined and conserved set of cellular pathways that respond to, limit, and repair the damage due to ROS. This adaptive set of genes are called the phase II system. They encode enzymes that degrade ROS directly as well as increase levels of cells' endogenous antioxidant molecules, including glutathione and bilirubin.
Of the phase II enzyme system, HMOX1, a human gene that encodes for the enzyme heme oxygenase 1, has been found to be a key component. The role of HMOX1 is to metabolize heme into bilirubin, carbon monoxide, and free iron by a two-step process. The first and rate-limiting step is the production of biliverdin and carbon monoxide from heme by HMOX1. The second step is the production of bilirubin from biliverdin by biliverdin reductase. Both bilirubin and carbon monoxide have been shown to scavenge ROS and to have potent anti-oxidant and anti-inflammatory activities.
Agents that induce production of HMOX1 have been shown to have beneficial activity in models of diabetes, cardiovascular disease, hypertension, and pulmonary function. Heme, heavy metal ions (e.g., arsenite, cadmium, iron, lead, chromium and mercury), and electrophiles (e.g., natural products such as sulforaphane and curcumin) can all induce production of HMOX1. Induction of HMOX1 and other phase II genes are controlled by a number of transcription factors that are responsive to heavy metals, heme, and electrophiles. The transcription factors Nrf2, Bach1, and small Maf proteins are particularly important in this process. For example, a common sequence called antioxidant responsive element (ARE) is present in a promoter of each gene of the phase II enzymes, and its expression is induced by the transcription factor Nrf2 (NF-E2 related factor 2).
HMOX1 is also induced as part of a generalized stress response to stimuli such as thermal shock, oxidative stress and cytokines such as interleukin-1 (IL-1), tumor necrosis factor and interleukin-6 (IL-6). This stress response is seen as beneficial in that it results in protection of vulnerable cells from multiple insults.
It has been reported that HMOX1 can be induced by small molecules that bind to the transcription factor Bach1. Heme binding to Bach1 has been shown to reduce DNA binding activity of Bach1 and induce gene transcription. See Ogawa K et al. EMBO J (2001) 20:2835-284. Additionally, a small molecule has been reported to induce HMOX1 through binding to Bach1. See Attucks O C et al. PLOS ONE (2014) 9(7): e101044, WO2011/103018 and WO2012/094580.
As such, there is a need for new HMOX1 inducers and/or Bach 1 binders/inhibitors for the above referenced therapeutic indications.